Coherence protection and microwave spin manipulation of tin vacancy centers in strained diamond membrane*

Group IV color centers in diamond, such as silicon- and tin-vacancy centers, are prime candidates for quantum networking nodes due to their exceptional optical and spin properties with the choice of integrated long-lived spin memories. However, each group IV center comes with trade-offs between elevated operation temperature beyond sub-Kelvin and fast, high fidelity microwave spin manipulation. In this work, we introduce a new platform to address this incompatibility: tin vacancy centers in strained diamond membranes. Thermally induced crystal strain between diamond and carrier substrate introduces orbital mixing between electronic spin states that allows power efficient microwave control with a Rabi π-gate fidelity of 99.4%. The strain-induced separation between orbital branches suppresses the temperature-dependent dephasing process, leading to a considerable improvement of the coherence time beyond a millisecond at 1.7 Kelvin and up to 223 µs at 4 Kelvin, a widely accessible temperature in common cryogenic systems. Critically, the coherence of optical transitions exhibits nearly constant, lifetime-limited optical linewidths with temperature up to 7 Kelvin. Combined with additional strain profile engineering of diamond membrane heterostructures, the demonstrated platform is a promising spin-photon interface for quantum networking applications.